In producing blow molded hollow members of thermoplastic material such as large drums, it is desirable to form chimes projecting radially outwardly of the hollow member adjacent each end thereof. These chimes facilitate handling, rolling and hoisting of the hollow member. With hollow drums blow molded from thermoplastic material, it is technically difficult to separately prepare top and bottom chime members. Accordingly, blow molded drums have been initially blow molded from a parison with a radially outwardly projecting annular channel-shaped part. The end members of the mold parts in which the blow molding operation occurs have been constructed to move axially so as to manipulate the material of the channel-shaped part into the shape of a chime. A mold construction of this type is discussed in allowed copending application Ser. No. 884,397 now U.S. Pat. No. 4,228,122 issued Oct. 14, 1980.
A disadvantage of this type of structure resides in the tendency of the material in the channel-shaped part to be forced inwardly of the hollow drum member during forming of the chime. This is a result of the compressive movement of the mold parts on the plastic material of the channel-shaped part and it causes the material to fold over on itself and form several layers one adhering to the other. Also, in the vicinity of the vertical side seams of the mold halves where the wall of the blow molded member is of increased thickness, the excess material tends to bulge into the interior of the hollow member during formation of the chime. As the material cools, different shrinkage tensions occur as a result of differential material accumulations, to which are added the tensions in the sandwiched layers. In the use of such a drum member, cracks can develop at these points.